Referring to FIG. 1, a prior art electret condenser microphone used with headsets and handsets is illustrated. A cylindrical housing capsule 102 holds the various components of the microphone. Housing capsule 102 includes a port 104 on the upper surface facing a 106. Voice signals are transmitted through port 104 to impinge on 106. A backplate 112 is fixed just behind port 104. A capacitance gap exists between 106 and backplate 112. A ring diaphragm spacer 110 is placed between 106 and backplate 112 to create the capacitance gap between 106 and backplate 112. A dielectric holder 114, FET 116, and PCB 118 are in the lower part of housing capsule 102. Housing capsule 102 is crimped to PCB 118. An input lead of FET 116 is coupled to backplate 112, and output lead is coupled to PCB 118. A cloth cover 120 may be placed over port 104 to prevent undesirable matter from entering the housing capsule 102 through port 104. In operation, sound waves impinge on diaphragm 106 causing diaphragm 106 to vibrate, thereby changing the capacitance between the diaphragm and fixed electrode in proportion to the strength of the sound waves. The change in capacitance is converted to a current or voltage change using FET 116.
Portable telephonic devices are often used in a wide variety of locations. Such use includes outdoor locations in less than ideal circumstances where wind is present. Wind adversely affects the performance of microphones in headsets or phones, manifesting itself in wind noise. Noise caused by wind in a microphone may result from passage of wind (moving air) or a person's breath that has entered the microphone port over the microphone diaphragm, causing the diaphragm to vibrate. Wind impinging on diaphragm 106 will be detected by the microphone along with the desired user speech and integrated into the microphone output signal as a low frequency signal component. The low frequency signal components will result in an audible rumbling noise at a receiver end, affecting the intelligibility of the user speech. Wind noise may also result from the sudden stoppage of the wind in the vicinity of the microphone diaphragm, such as at the edges of the port, or the passage of wind over the port and subsequent interaction with the edges of the port.
In the prior art, several attempts have been made to reduce the effects of wind noise. For example, telephone handsets have utilized windscreens placed in front of the microphone to prevent wind from impinging upon the microphone diaphragm. However, such wind screens are often bulky and aesthetically displeasing. Furthermore, windscreens may affect pickup of the desired speech signal. Such windscreens are particularly inconvenient when used with headsets, where considerations such as ease of portability, storage, and damage resistance increase in importance. In addition to windscreens, prior art solutions have utilized post FET output signal processing to filter out low frequency wind noise components of signal. However, because the wind noise still impinges on the diaphragm, the noise may overload the FET or cause excessive motion of the diaphragm, thereby reducing the quality of the detected speech signal. Still another prior art method involves placing a controlled perforation in the diaphragm to create a high pass filter function. Problems with this solution include sensitivity loss due to a reduction in the metallized area of the diaphragms, as well as the requirement of an additional step in the assembly process.
Thus, improved designs for telephonic devices with reduced sensitivity to wind noise are needed. In particular, there is a need for improved microphones that minimize the pickup of wind noise.